This invention relates to a developing device for an electrophotographic image formation apparatus such as a copier and a laser printer for applying toner to an electrostatic latent image formed on a photoreceptor by exposure thereof to an image-forming beam of light.
A photoreceptor of the type most commonly used in electrophotography is cylindrical in shape and is frequently referred to simply as a drum. A developer roller for forming a magnetic brush on its surface is disposed parallel to such a cylindrical photoreceptor and means for supplying toner to this developer roller is usually disposed thereabove and extending parallel thereto. With the toner supply means thus disposed along the axis of the developer roller, however, care must be taken such that the image forming beam is not blocked thereby and prevented from reaching the photoreceptor so as to form an electrostatic latent image thereon. In view of the above, the region which is exposed to the incident beam and the region where development takes place by the developer roller are separated by a large distance, but this does not allow the copier to be designed compactly.
A developing device is usually comprised of a housing and a container for containing a fresh supply of developing agent to be supplied into the housing which includes not only a developing tank containing the aforementioned developer roller and a supply tank for supplying developing agent into the developing tank. When the copier is used for monochromatic printing in a different color, however, the user must normally remove the entire developing device with both its housing and its container and replace it by another one for the desired color. Since the developing device is not small, it is a cumbersome job to exchange developing devices and a large space is required to store a removed developing device.